Petroleum wells can be naturally flowing, injecting or can be produced by any means of artificial lift. Such artificial lift in a production well may be produced by, but is not limited to, an electrical submersible pump (ESP), a sucker rod pump, and/or a progressing cavity pump. For instance, an ESP system may include an electric motor and a pump that is used to pump oil or other liquids within a wellbore. The electric motor may have a rotatable rotor that is contained in a stationary stator. When the motor operates, the rotor may rotate to provide artificial lift within the wellbore.
Referring to FIG. 1, a diagram of a typical ESP system (100) includes a centrifugal pump (101), a pump motor (105), and a seal assembly (103) located between the pump (101) and motor (105). The pump (101), seal assembly (103), and motor (105) are located within a borehole (121), inside a standard well casing (123). The ESP system (100) further includes a variable speed drive (111), a controller (113), and an optional transformer (115) located on the surface (125). A three-phase power cable (117) provides power and communications between the variable speed drive (111) (or optional transformer (115)) and the pump motor (105). The variable speed drive (111) can operate as a power source by providing electrical power for driving the motor (105). The cable (117) typically extends thousands of feet and thereby introduces significant electrical impedance between the variable speed drive (111) (or optional transformer (115)) and the pump motor (105). By altering the output voltage and frequency of the variable speed drive (111), the controller (113) associated with the variable speed drive (111) controls the voltage at motor (105) terminals, and thus the operation of the pump.
As can be seen from FIG. 1, where the product flowing into the well bore contains entrained and free gas, that gas can enter the pump and reduce the volumetric efficiency of the pump. For instance, the hydrocarbon production stream can include both liquid and gaseous products that are a natural byproduct of the producing wells. As hydrocarbons and water flow through the formation, gases can travel in the flow stream either separate from the liquid products or dissolved within the liquid products. The gases are carried into the production tubing and can cause problems for an artificial lifting mechanism, such as ESP systems, by reducing the volumetric efficiency of the pump.
Gas interference occurs in situations when the pump is filling with a considerable amount of free gas that is not separated before entering the pump. If the amount of free gas entering the pump can be reduced, the volumetric efficiency of the pump can be improved, or the total pump capacity can be increased.